I. Field of the Invention
The present invention relates generally to the treatment and prevention of cancer. The methods and compositions of this invention comprise the use of small molecules as ligands for binding to TRAIL-R1/DR4 and/or TRAIL-R2/DR5 death receptors, the recruitment of FADD (Fas-associated death domain protein), the activation of the death-inducing signaling complex (DISC), the activating of caspase-8, and the induction apoptosis in malignant cells. The methods and compositions of this invention may be used for the treatment and/or prevention of a variety of diseases, such as those where excess cell growth is a problem.
II. Description of Related Art
Apoptosis is a genetically programmed cell death that is required for morphogenesis during embryogenic development and for tissue homeostasis in adult organisms. Failure to undergo apoptosis has been implicated in tumor development and resistance to cancer therapy. Dysregulation of the apoptotic machinery plays a role in the pathogenesis of various diseases and molecules involved in cell death pathways are potential therapeutic targets in immunologic, neurologic, cancer, infectious and inflammatory diseases. Strategies for overcoming resistance to apoptosis include direct targeting of antiapoptotic molecules expressed in tumors, re-sensitization of previously resistant tumor cells by counteracting survival pathways and inducing expression or activity of proapoptotic molecules.
Most chemotherapeutic drugs can induce tumor cell death by apoptosis. Analysis of the molecular mechanisms that regulate apoptosis indicates that anticancer agents simultaneously activate several pathways that either positively or negatively regulate the death process. The main pathway of apoptosis induced by drugs involves activation of caspases in the cytosol by pro-apoptotic molecules. At least in some cell types, anticancer drugs also upregulate the expression of death receptors and sensitize tumor cells to their cognate ligands (Singh et al., 2003). In some cases, the Fas-mediated pathway contributes to the early steps of drug-induced apoptosis while sensitization to the cytokine TRAIL can be used to amplify the response to cytotoxic drugs.
The Bcl-2 family of proteins, that includes anti- and pro-apoptotic molecules, regulates cell sensitivity mainly at the mitochondrial level (Green and Reed, 1998; Singh et al., 2003). Anticancer drugs modulate their expression (e.g. through p53-dependent gene transcription), their activity (e.g. by phosphorylating Bcl-2) and their subcellular localization (e.g. by inducing translocation of pro-apoptotic proteins). Very early after interacting with tumor cells, anticancer drugs also activate lipid-dependent signaling pathways that increase or decrease apoptosis. In addition, cytotoxic agents can activate protective pathways that involve activation of NFκB transcription factor, Akt protein kinase and proteins involved in cell cycle regulation (e.g. cyclin D1), and accumulation of heat shock proteins such as Hsp27.
TNF-related apoptosis-inducing ligand (TRAIL) is a ligand molecule which induces the process of cell death called apoptosis. It is a type II transmembrane protein with homology to other members of the tumor necrosis factor (TNF) family. There are a number of ligand-receptor families that are involved in apoptosis. Some of the members of this family are TNF-α, CD95L/FasL/APO-1L, and TRAIL/APO-2L (TRAIL=TNF related apoptosis inducing ligand.). They regulate many biological functions including cell metabolism, proliferation, cytokine production and apoptosis (Krammer, 1999; Pitti et al., 1996; Wiley et al., 1995). TRAIL/APO-2L specifically kills transformed and cancer cells via binding with specific cell-surface death receptors (TRAIL-R1/DR4 and TRAIL-R2/DR5). Most normal cells appear to be resistant to TRAIL activation (Ashkenazi and Dixit, 1999; Chen et al., 2001; Singh et al., 2003; Walczak et al., 1999), suggesting a higher activity of TRAIL with its receptors on tumor cells. Binding of DR4 or DR5 with TRAIL results in a caspase-activating signal leading to apoptosis (French and Tschopp, 2003; LeBlanc and Ashkenazi, 2003; Srivastava, 2001). Recent studies have shown that systemic administration of TRAIL in 60 mice is physiologically safe, effective in killing human breast, prostate and colon tumor xenografts, and prolongs survival of tumor-bearing mice (French and Tschopp, 1999; Ray and Almasan, 2003; Shankar et al., 2004a,b; Singh et al., 2003). TRAIL participates in cytotoxicity mediated by activated NK cells (Kayagaki et al., 1999a), monocytes (Griffith et al., 1999) and some cytotoxic T cells (Kayagaki et al., 1999b; Thomas and Hersey, 1998).
Current approaches for the development of TRAIL-R1 and/or TRAIL-R2 agonists as anticancer agents include the use of monoclonal antibodies, as discussed in WO/2079377, and targeting of the receptor(s) using a soluble form of TRAIL. Given the drawback of monoclonal antibodies and polypeptide therapeutics, new strategies for treating cancer by targeting death receptor pathway are desirable.